1. Field of the Invention
This invention relates generally to the detection, identification and quantification of the chemical warfare agent commonly referred to as “VX”,(methylphosphonothioic acid, having the chemical formula, [O-ethyl S-(2-diisopropylaminoethyl) methyl phosphonothiolate]). More particularly, the present invention concerns air monitoring systems that facilitate detection of the chemical warfare agent VX by converting VX into its G Analog, which is easier to detect and works more efficiently with systems that are currently in use in many disciplines of chemical warfare agent detection, identification and quantification. Even more specifically, the present invention concerns improved sampling and analytical apparatus and methods to be used in or near chemical warfare agent manufacturing or handling facilities, in or near chemical warfare agent demilitarization facilities, at perimeter sampling sites strategically located near such facilities, and at battlefields or any environments where chemical warfare agents may be present. The present invention has applications in a wide variety of situations, including challenge testing for gas chromatographs to facilitate the monitoring or testing for gases, liquids and residues of VX as well as other similar chemical warfare agents.
2. Description of the Prior Art
Nerve agents are chemical compounds, which affect the central nervous system of animal life. These nerve agent compounds were originally derived from pesticide development work originally done in Germany. The physiological effect of nerve agents in man and other animal life is the interruption of nerve impulses along the central nervous system, thus disturbing essential body functions, such as breathing, vision and muscular control, and potentially causing death. As mentioned above, the principal nerve agent of interest from the standpoint of chemical warfare agent detection according to the present invention is “VX”, (methylphosphonothioic acid, having the chemical formula, [O-ethyl S-(2-diisopropylaminoethyl) methyl phosphonothiolate]). Though the present invention is described in detail here, particularly as it relates to detection and quantification of the nerve agent VX, it is to be borne in mind that it is not intended that the present invention be restricted solely to its association with the nerve agent VX, but rather that the present invention be applicable to facilitate simple, efficient and low cost sampling for the presence of any similar chemical warfare agent or compound with which the present invention is capable of effective use. For example, under certain circumstances the present invention will find effective use for achieving samples of other nerve agents, particularly “GB” and “HD” as well as other nerve agents and chemical warfare agents that are not currently known in detail in the United States. Thus, when the agent “VX” is mentioned herein, it is intended that the present invention will be applicable to the agent VX and to any other nerve agent or chemical warfare agent that may be utilized in chemical warfare. Other chemical warfare agents of interest from the standpoint of the present invention are Phosphonothioic acid, methyl-, S-(2-bis(1-methylethylamino)ethyl) 0-ethyl ester O-ethyl; S-(2-diisopropylaminoethyl) methylphosphonothiolate; S-2-Diisopropylaminoethyl O-ethyl methylphosphonothioate; S-2((2-Diisopropylamino)ethyl) O-ethyl methylphosphonothiolate; O-ethyl S-(2-diisopropylaminoethyl) methylphosphonothioate; O-ethyl S-(2-diisopropylaminoethyl) methylthiolphosphonoate; S-(2-diisopropylaminoethyl) o-ethyl methyl phosphonothiolate; Ethyl-S-dimethylaminoethyl methylphosphonothiolate VX EA 1701; and TX60
The nerve agent “VX” acts on the body by inhibiting the enzyme cholinesterase. When this enzyme is prevented from working, nerves react uncontrollably, interrupting essential body functions such as breathing, vision and muscular control, and potentially causing death. The principal route of exposure to “VX” is via absorption through the skin, though it can also be absorbed by the digestive tract or by the respiratory tract if in vapor or aerosol form.
In the past 5 years, new methods and systems for monitoring chemical warfare agents have increased, and many of the methods and systems require taking air samples from a given location or environment and transporting the air sample through sample lines and into an adsorbent tube, known as a Depot Area Air Monitoring System tube (DAAMS tube), for later analysis, or directly onto a suitable type of chemical detector, such as a surface acoustic wave detector, a gas chromatograph or any number of other detectors often associated with but not limited to chromatography. The US Government is currently destroying its chemical weapons stockpiles in specified demilitarization plants, and stringent safety standards are imposed on all operations involving chemical warfare agents. These safety standards are intended to protect the demilitarization plant workers and also to protect the general public from accidental exposure to harmful levels of chemical warfare agents. Adequate chemical analysis procedures for the determination of the presence of chemical warfare agents in work areas, in the perimeter air of chemical warfare agent handling facilities and in the various plant effluents of such facilities are critical aspects of the U.S. Government's safety program. Samples of work area and perimeter air surrounding a chemical warfare handling facility area and samples of various effluents (gases, liquids, and solids) must be regularly and routinely collected and analyzed to certify that they do not contain chemical warfare agents at concentrations exceeding the limits established by the US Surgeon General. Chemical warfare agents are becoming an increasing worldwide concern, and in many different countries both military and civilian agencies and communities are beginning to do independent chemical agent analysis of their environments to detect and identify the presence of chemical warfare agents and the source or origin thereof. More specifically, these countries, including the United States, have initiated monitoring for chemical warfare agents for the safety of their communities. The analytical methods currently used by the U.S. Government for the determination of trace quantities of VX generally comprise air monitoring by collecting samples of atmospheric or stack-gases.
According to the basic methodology for the Depot Area Air Monitoring System (DAAMS) determination of VX, because the gas-chromatographic determination of trace quantities of VX is not a straightforward matter, agent VX is converted to its G-analog (ethyl methylphosphonofluoridate) before it is collected for analysis according to DAAMS procedures. Conversion of agent VX to its G-analog is accomplished by passing the sample (gas, liquid, solid or combination thereof) through an AgN03/KF-impregnated polyester filter (V-to-G conversion filter) connected to the inlet end of the sorbent tube. The conversion of VX to its G-analog can be illustrated by the following reaction:

Chemical warfare agent sampling apparatus has been developed using a fitting which is intended for releasable mounting of AgNO3/KF impregnated filter elements or circles through which environmental air is drawn for conversion of any VX chemical warfare agent content to its G-analog. To ensure the functionality of a gas chromatograph, the conversion filters are frequently challenged with a solution having a known quantity of the chemical warfare agent VX, which is converted to its G-analog and then conducted to the detector of a gas chromatograph, where it is detected and quantified. It has been determined that conversion filters for the determination of VX as its G-analog function quite well when prepared by impregnating a typically non-woven fibrous material with AgNO3/KF. A backup filter of the same or different fibrous filter material in non-impregnated form has been located at the downstream end of the impregnated filter material in order to prevent flakes of the conversion reagent from being swept from the conversion filter into the sampling tube or apparatus along with the air being drawn through the conversion filters by the vacuum source that is typically used. In the past, as shown in FIG. 9,and identified as “Prior Art”, conversion filters, impregnated with AgNO3/KF, for conversion of VX were inserted into a compression fitting, typically at the inlet end and secured by a ferrule and nut assembly of the fitting. This was a difficult and time-consuming task, since the conversion filters are quite small, being in the order of from about 3/16 inch to about 1 inch in diameter and having a thickness in the order of about 1/16 inch, and also because the worker's hands may be gloved and protective garments may be worn, especially if the presence of VX is known or suspected. The conversion filter assembly, including the impregnated and non-impregnated filter substrates, were then secured within the fitting with the compression nut at the inlet of the fitting. If the conversion filter assembly is to be removed for replacement, the compression nut and ferrule assembly must be removed and the small filter elements are typically manually removed from the fitting. Thus, filter replacement has been a time-consuming and labor intensive process, adding significantly to the time, cost and difficulty of the chemical warfare agent testing process.
With a conversion filter assembly in place, the converted G analog of the VX in the sample is then conducted to a DAAMS tube, to a gas chromatograph or to any other sample detection and measurement system that is being utilized.
It is necessary to effect formal compliance with regulations concerning chemical warfare agent sampling procedures, including that the parameters of each sample, such as lot number, date of preparation, date of installation, date of removal, identity of specific constituents, etc. be recorded, so that controlled identification and tracking of chemical warfare agent samples can be accomplished. According to sampling procedures presently in use, the conversion filters and backup filters cannot be labeled. Thus, they must be placed in special containers that can be labeled and placed in a tracking system. In sum, there is the possibility for significant error in labeling and component identification that complicates and enhances the cost, as well as influencing the reliability of the chemical warfare agent sampling procedure. Therefore, it is desirable to provide a chemical warfare agent sampling procedure that efficiently facilitates labeling and tracking of samples.